An idea just flashed into my mind when I was in bathroom.
See the illustration I posted before.
Isn't it a proof that the vertices positions are saved properly? But it is strange that they displaced if they are not in horizontal or vertical line and it is contradicting to the trick we was thinking of.
I think we need to test in a more detailed way. I will check the eye, head, hair_0, hair_1 of a few models and write down the variation of the exported vertices positions. From my own experience, visually, the displacement of vertices only happens on hair models. I will tell you the results no longer than next weekend.
Thanks for your hard work mate!